Alternating current circuit interrupter



y 13, 1939- F. L. STONE ALTERNATING CURRENT CIRCUIT INTERRUPTER Filed June 28, 1938 Patented July 18, 1939 My invention relates to circuit interrupters, more particularly to alternating current circuit interrupters, and has for its principal object the provision of an improved alternating current are interrupter that is effective to interrupt arcing without causing appreciable extension or lengthenlng of the arc beyond the arc gap determined by separation of the interrupter electrodes or It is well known that the arc energyincreases with increase in the length of the arc, and that such increase in energy is often undesirable since it requires the dissipation of a considerable amount of heat during the arc-interrupting operation. However, this method of arc interruption is commonly used in the conventional magnetic blow-out type breaker since lengthening and subsequent cooling of the arc within the arc chute are also relied upon to increase the arc resistance so that interruption can take place at a current zero In this type of breaker, a blow-out coil in series with the circuit to be interrupted is usually employed so that the alternating magnetic blow-out flux, causes continuous transverse movement of the are through the chute. Accordingly, the arc is extended or looped into the chute so as appreciably to increase the arc length and, consequently, the heat to be dis- In accordance with the present invention, an alternating current are is subjected to a substantially constant and direct or unidirectional blow-out flux whereby the arc, instead of being extended or moved continuously in a transverse direction, is subjected to a force tending to oscillate it within comparatively narrow limits at a rate corresponding to the frequency of the are If not interrupted at the first current zero due to the presence of a. large and constant blow-out flux, the rapid oscillation of the arc and are roots across the contact surfaces serves to deionize the arc and to facilitate interruption within substantially the arc length determined by the gap formed by the separated interrupter electrodes, or contacts.

My invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. 1 is a partly diagrammatic view of an alternating current circuit breaker embodying the present invention, Fig. 2 is an end view of the breaker shown in Fig. 1,

UNITED STATES PATENT OFFICE ALTEBNATING CURRENT CIRCUIT INTERQRUP'IER.

Fred L. Stone, Schenectady, N. Y., assignor to General Electric Company, a corporation of Application June 28, 1938, Serial No. 218,271

and Fig. 3 is a side elevational view partly broken away of another form my invention may assume.

In the interrupting arrangement shown by Figs. 1 and 2 a load circuit I for supplying current to apparatus, such as a motor 2, is energized from I an alternating current power circuit indicated at 3. A circuit breaker embodying the present invention is indicated at 4 for controlling the load circuit I, and comprises in the present instance a pair of relatively movable contacts 5 and 6 op- 10 erable within an insulating housing I that is open at the opposite ends thereof as illustrated. The load circuit I is suitably connected to the breaker contacts by the terminals 4'.

The contacts 5 and 6 in the specific arrange- 5 ment shown are arcuate in form and are adapted to engage in abutting contact at the surfaces 5' and 6' respectively in the closed circuit position.

In the open circuit position shown the fixed contact 5 and the coacting movable contact 6 form 80 with the insulating housing I a pair of oppositely extending diverging arc passages extending from the arc gap defined by the contact surfaces 5' and 6'. Accordingly, when the breaker is opened by downward movement of the contact 6 to the position shown, an arc is formed at the central or narrowed part of the arc passage.

For the purpose of interrupting the arc in the manner above described, a magnet core 8 having depending pole pieces 9 extending along the insuiting housing I at opposite sides of the arc gap is provided with an energizing coil III that is connected in any suitable manner with a direct current source. In the present instance, the coil I0 is shown diagrammatically as energized from the main alternating current power circuit through a full wave rectifier II. The flux between the pole pieces 9 across the arc gap 5'-6 is therefore direct or unidirectional in character as contrasted with the alternating arc current and furthermore is not dependent on the magnitude of the arc current. This is an advantage Where the arc current is weak.

Accordingly, when the alternating current are is formed the unidirectional flux tends to oscillate the are as long as it persists back and forth within the arc passage between the contacts 5 and B. The rate of oscillation is of course dependent on the frequency of the circuit to be interrupted. Coincident with the oscillation of the arc and the deionizing tendency, thearc roots themselves are rapidly moved back and forth along the conducting surfaces of the contacts 5 and 6 so that the formation of metallic vapor is minimized. This is an important consideration since intertion of the are are undoubtedly present.

.tion hardened alloy type.

ruption of the arc is made more difilcult by the presence of a large amount oimetallic vapor caused by a stationary arc root. Rapid oscillation of the arc roots also serves to increase the life of the contacts.

The deionizing efiect of rapidly oscillating the are by a substantially constant and steady fiux within predetermined limits is an important factor in causing interruption of the arc although other factors likewise tending to cause extinc- The above deionizing effect is of course enhanced by the presence of the strong blow-out flux when the arc current passes through the zero value. This is not the case in the conventional magnetic blowout breaker.

It will be observed that lengthening of the arc is limited in a positive manner by the arc gap defined between the contacts 5 and '6 within the insulating housing. Even assuming appreciable amplitude of oscillation within the arc passage i it will be apparent that the actual arc length is not at any time greatly in excess of the minimum arc gap. Furthermore, .the well known tendency of the a'rc to loop outwardly along a horn gap is counteracted at the subsequent half cycle when the arc is subjected to. a force causing it to move in the opposite direction. This serves, as above pointed out, to minimize the arc energy generated during the interrupting operation and hence to facilitate interruption.

Movement of the contact 6 can be effected in any suitable manner, a simple arrangement being diagrammatically illustrated for this purpose.

-A closing solenoid I2 is connected through an operating rod l3 and a resilient or wipe con-nection at I4 to the contact 6. The solenoid l2 can be energized from the source 3 through a push button control iii to close the breaker, the same .being heldin closed circuit position by a latch and detent lfi-ll. In case of overload on the load circuit i a current transformer I8 causes energization of the trip coil l9 so as to actuate the releasing latch l6 whereupon the contact 6 moves downward to the open circuit position shown.

Fig. 3 illustrates a simplified form of the alternating current are interrupter wherein the constant unidirectional magnetic flux is produced by a permanent magnet, preferably of the precipita- This type of permanent magnet has a comparatively large magnetomotive force and is particularly eifect'ive at low values of the arc current, as'contrasted with the conventional magnetic blow-out air circuit break- .er wherein the blow-out flux is obviously dependent on the magnitude of the current to be interstantially the same as described in connection.

. with Figs. 1 and 2. In this case, however, a

.permanent magnet 20 having depending pole pieces 2| extending along opposite sides'of the arc gap between the contacts 5 and 6 is provided.

A permanent magnet of the character above described is effective to project a strong, constant unidirectional flux across the arc gap at all values of the arc current so that the arc is oscillated in the manner above described at a rate corresponding to the frequency of the arc current.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An alternating current are interrupter comprising arc forming means for defining an arc gap, means for subjecting the arc in said gap to a unidirectional flux whereby said are tends to oscillate with respect to said gap'at a rate corresponding to the frequency of the arc current, and means for maintaining said are in said gap substantially at constant length.

2. An alternating current are interrupter comprising are forming means for defining an arc gap of substantially predetermined length, means for subjecting the arc in said gap to a substantially constant unidirectional flux whereby said are tends to oscillate in said gap at a rate corresponding to the frequency of the arc current, and means for restricting said are to a length not appreciably in excess of the width of said gap.

3. An alternating current arc' 'lnterrupter comprising are forming means for defining an arc gap, ,a magnet for projecting a substantially steady, constant and unidirectional flux across said gap whereby said are and the roots thereof tend to oscillate within said gap at a rate corresponding to the frequency of the arc current,

.thereof, and magnetic means for projecting a substantially constant unidirectional flux across the minimum gap whereby said are and the roots thereof tend to oscillate with respect to said minimum gap at a rate corresponding to the frequency of the arc current, said unidirectional flux being related to said electrodes so that said are is restricted to a length not appreciably in excess of the width of said gaps.

5. An alternating current are interrupter comprising coacting electrodes for defining an arc stantially constant magnetomotive force for projecting a unidirectional flux across said gap so that said are is acted upon by an oscillating force, said flux being of blow-out magnitude in said gap when the arc current passes through the zero value, and means for restricting said arcto a length not appreciably in excess of the width of said gap.

6. An alternating current are interrupter comprising a pair of elongated contacts separable transversely of the longitudinal axes thereof to form an arc gap, and a permanent magnet having poles extending along opposite sides of said gap for projecting a constant unidirectional flux across said gap whereby said are is subjected to an oscillating force tending toprevent appreci able lengthening thereof..

FRED L. STONE. 

